noskowicz



Feb. 7, 1956 T. S. NOSKOWICZ Filed July 21, 1953 2 Sheets-Sheet l ,ll ,|4 it R.F. Amp. Low-Pass 8i First Filter Detector 1, I9 20 23 E I l r I I. F. Color Blue Low- Pass Amplifier Reference Demodul. Filter Generator Image l l r l Reproducer Second Band-Poss Inverter Detector Filter Mixer l ,m l ,21 l ,25 Sync. Scanning Red Low-Pass Signal Signal Demodul. Filter Separator Generator l4 Low-Pass Filter 23'-Low-Poss Filter l 24 lnverter' Mixer 25- Low-Pass Filter Scanning Signal Generator 3 1 4s FIG. 2 43 THEODORE S. NOSKOWICZ IN VEN TOR.

HIS ATTORNEY Feb. 7, 1956 'r. s. NOSKOWICZ IMAGE-REPRODUCING DEVICES 2 Sheets-Sheet 2 FIG?) Filed July 21, 1953 THEODORE S. NOSKOWICZ IN V EN TOR.

HIS ATTORN IMAGE-REPRODUCING DEVICES Theodore S. Noskowicz, Wood Dale, Ill., assignor to Rauland Corporation, acorporation of Illinois Application July 21, 1953, Serial No. 369,295

1 Claim. (Cl. 315) This invention relates to image-reproducing devices and more particularly to cathode-ray tubes used as picture reproducing devices in color television receivers and the like.

It is known that television images may be produced in simulated natural color through the use of an imagereproducing device having a target screen which is composed of a plurality of similar groups of elemental phosphor areas exhibiting different color response characteristics. The groups of phosphor elements may be arranged to constitute a series of triads individually including three phosphor elements which luminesce in the primary colors red, blue, and green. In order to effect a preselected energization of the phosphor elements of such triads, a parallax mask is interposed between the target and the electron-beam source of the tube. The parallax mask is constructed of an electrically conductive material containing a multiplicity of apertures arranged in a pattern which corresponds with that of the triads of color phosphors. These apertures are of sufiicient size to permit passage of an electron beam of appreciable cross-sectional area, and the path of the electron beam through the mask is controlled to cause the beam to approach the target from a different angle for each primary color. In this manner selective energization of the respective phosphors may be achieved.

The beam source of the tube may conveniently comprise three separate and distinct electron guns individually controlled by a color signal corresponding to one of three primary colors and so constructed and arranged that each beam approaches the target from a different angle. Equivalent operation may be achieved by employing a single electron gun controlled by a composite color signal and cooperating with an additional color-selective deflection system to cause the beam to approach the target from a different angle for each primary color.

One of the principal difficulties encountered in the use of color-image-reproducers of the parallax mask type lies in the fact that only about 15% of the electrons projected toward the target actually pass through the apertures of the parallax mask. This results from the fact that the diameter of each individual aperture is necessarily small relative to the beam diameter in order toprevent color contamination or excitation of color phosphors other than those intended'during any scansion of the target by the electron beam. Since a large percentage of the electrons are collected by the parallax mask, it may become distorted due to over-heating in operation, resulting in an enlargement of the apertures. This distortion may produce color contamination by allowing the electron beam to energize unintended phosphor areas; thus, the maximum permissible distortion from the point of view of color contamination imposes a serious limitation on the target voltage and therefore severely restricts the maximum obtainable picture brightness. I

,Another problem encountered in this general type of cathode-ray tube is attributable to the emission of secondary electrons from the parallax mask when post-selection r 2,734,146 Patented Feb. 7, 1956 acceleration is employed by placing a more elevated positive potential on the target than that applied to the parallax mask. Such post-selection acceleration may be desirable for the purpose of concentrating the electron beam between the target and the parallax mask, and for obtaining greater picture brightness. When this is done, however, any secondary electrons emitted from the parallax mask are drawn toward the target and may provoke undesired energization of the phosphor elements, thus impairing the fidelity of the color reproduction.

It is an object of the present invention, therefore, to provide a new and improved color-image reproducing device which avoids one or more of the above-mentioned limitations of prior devices.

Further objects of this invention are to provide a colorimage reproducing device of the parallax mask type in which overheating of the parallax mask, with the attendant color contamination and limitation on picture brightness, is effectively precluded, and to achieve this result through a simple and inexpensive modification of the construction of the image reproducer.

It is still another object of the invention to provide an improved color-image reproducer of the parallax grid type in which the adverse eifects of secondary electron emission, hitherto encountered when post-selection acceleration is employed to obtain increased picture brightness, are substantially avoided.

In accordance with the present invention, a new and improved image-reproducing device comprises a target assembly including a luminescent screen having interspersed similar phosphor groups of elemental target areas, and a parallax mask spaced from the luminescent screen. Each phosphor group consists of a predetermined plurality of elemental target areas and exhibits a distinctive colorresponse characteristic to electron bombardment. The parallax mask is provided with a plurality of electronpermeable areas, as for example apertures, each individually associated with one of the elemental target areas of each group. An electron-beam-producing structure, consisting of at least one electron gun, projects electrons toward the target assembly with different angles of approach to energize selectively the groups of target areas. An auxiliary blocking mask is interposed between the electron-beam structure and the target assembly and comprises an electrically conductive structure provided with a plurality of electron-permeable areas or apertures individually larger than the electron-permeable areas of the parallax mask and in registration with these latter areas. A potential difference is applied between the parallax mask and the luminescent screen, and the auxiliary blocking mask is maintained at a positive potential with respect to the parallax mask.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claim. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals indicate like elements, and in which:

Figure 1 is a block diagram of a color television receiver in which an image reproducer constructed in accordance with the invention may be employed,

Figure 2 is a schematic diagram of a portion of the receiver of Figure 1, including a cross-sectional view, partly schematic, of a color-image reproducing device constructed in accordance with the invention,

Figure 3 is an enlarged fragmentary view, partly schematic, of a portion of the image reproducer shown in Figure 2, and

Figure 4 is a partial cross-sectional view, partly cut away, taken along the line 4-4 of Figure 2.

The color television receiver illustrated in the block diagram of Figure l, and in which the color-image reproducer of the present invention is particularly, although not exclusively, useful may conveniently be of a known type constructed and arranged to receive N. T. S. C. (National Television Systems Committee) color television signals of the simultaneous type. A receiver of this type comprises an antenna coupled to a radiofrequency amplifier and first detector '11 which is connected in turn to an intermediate-frequency amplifier 12. Amplifier 12 is coupled to a second detector 13, the output of which is coupled to a low-pass filter 14, to a synchonizing-signal separator 15, and to a band-pass filter '22. Low-pass filter 1 4 is coupled to an image reproducer 17, which is preferably constructed in accordance with the invention as hereinafter described in detail.

Syncln'onizing-signal separator is coupled to a scanning-signal generator 18 which is connected to image reproducer l7 and to a color reference generator 19. The output of color reference generator 19 is coupled to a pair of color demodulators and 21, and band-pass filter 22- is also coupled to each of demodulators 20 and 21. Color demodulator 2% is coupled through a lowpass filter 23 to image reproducer 17 and to an invertermixer circuit 24. Demodulator 21 is similarly coupled to a low-pass filter 25, which in turn is connected to inverter-mixer 24 and to image reproducer 17; the output of circuit 24 is also coupled to the image reproducer.

The color television receiver shown in Figure 1 is conventioual in construction in all respects except for the improvement of the image reproducer, introduced by the present invention. Accordingly, a brief description of the overall receiver operation is deemed adequate. A modulated-carrier color-television signal is intercepted by antenna 1'1 and applied to circuit 11, wherein it is amplified and heterodyned with a locally generated signal to develop an intermediate-frequency color television signal. The intermediate-frequency signal is amplified in amplifier 12 and applied to second detector 13, which utilizes the intermediate-frequency signal to develop a composite color signal comprising periodically recurring synchronizing-signal components and interspersed color picture components. The synchronizing-signal components include scanning repetition frequency information as well as bursts of a color sync signal having a frequency equal to the frequency of the color subcarrier signal and having a fixed phase relationship with respect to the color subcarrier signal. The composite color video signal developed in second detector 13 is supplied to filter 14, which translates only those portions of the composite color video signal generally corresponding to the luminance information to image reproducer 17. The composite color video signal is also applied to separator 15, which segregates the synchronizing-signal components and applies those components to generator 18 to control the frequency of locally generated scanningsignal's which are supplied to reproducer 17. In addition, the color sync signal or color bursts, which form a part of the synchronizing-signal components are supplied to color reference generator 19 from separator 15 and are utilized to control the generation of a color carrier reference signal which is applied in predetermined phase relation to demodulator 20 and inpredetermined different phase relation to demodulator 21. That portion of the color picture signal comprising chrominance information is translated from second detector 13 through filter 22 and applied to demodulators 20 and 21. In'demodulator 20, here designated the blue demodulator, the chrominance information suppliedfrom filter '22 is demodulated by means of the color reference signal supplied from generator 19 to develop 'a first color difference signal "B-Y. Similarly, in red demodulator 21, the'chrominan'ceinformation is heterodyned with the color carrier reference signal'to develop a second color differencesignal vR-Y. The color differencesignals are translated through 10W- pass filters 23 and 25 and are supplied to image reproducer -17 to control the color content of the reproduced respect to a third primary color.

The requisite power supplies and audio circuits have not been shown or described as they are of conventional design.

For simplicity in illustrating one of the preferred embodiments of the present invention, Figure 2 discloses only a portion of the color television receiver of Figure 1, including an image reproducer constructed in accordance with the invention. In Figure 2, an evacuated envelope 34 encloses an electron gun assembly 31, here shown for convenience as comprising three separate electron guns, each of which includes a cathode, a control grid, and suitable accelerating and focusing anodes to produce an electron stream, directed through a parallax grid 33 toward a fluorescent screen or target 41. The structural arrangement of the three gun electron source is such that the electron beam produced in each gun approaches target 41 from a different angle. The electron guns, which may be associated with an individual color component of the received television signal, are geometrically located apart about the tube axis at the vertices of an equilateral triangle. Low-pass filter 23, inverter-mixer 24 and low-pass filter 25 are individually coupled to a control grid of one of the electron guns of the tri-gun assembly 31, while low-pass filter 14 is coupled to the control grids of all three guns of electron gun assembly 31. A convergence coil 32 surrounds the neck of the evacuated envelope 34 at a point between gun structure 31 and a conventional deflecting and focusing coil assembly or yoke 33, which similarly encompass a portion of the neck of image reproducer 17. Coil 32 is energized from 'a suitable source (not shown) to provide dynamic convergence for the three separate electron beams so that the beams, which are 120 degrees apart about the axis of the tube, are converged to 'a point in the plane of the parallax mask 38. Scanning-signal generator 18 is coupled to deflection and focusing coil assembly 33. The envelope comprises a conical portion 35 constructed of metal, glass coated with a conductive material such as colloidal graphite, or the like to constitute a common final anode for all three electron guns.

Target 41 comprises a plurality of interspersed similar groups of similar elemental phosphor areas; in the conventional tube, three such groups are employed. These groups are formed of phosphors respectively corresponding to the three primary colors and may be arranged in such manner that the elemental phosphor areas appear in the configuration of triads each consisting of one elemental area of each of the three phosphors. Techniques of forming the tricolor target are Well known and constitute no part of the present invention; consequently no further explanation of the target construction is required. Parallax mask 38 consists of a screen provided with a plurality of electron-permeable areas 40, preferably in the form of apertures. Each of these apertures is associated with a triadgroup of the elemental phosphor areas so that an electron beam passing through each aperture may be controlled to energize one of the elemental phosphor areas. Elementalrphosphor groups may be separately energized to emit light of apreselected wavelength by the selection of the angle of approach of the electron beam through the parallax mask. A suitable source of direct potential, here shown as a battery 43, is coupled to parallax mask 38 through a wire or other electrically conductive structure 45 to maintain its surface at a suitable operating bias, potential. Voltage source 43 maybe of any conventional design and may comprise a voltage rectifier operating on the A. C. line current or driven from the power amplifier stage of scanning-signal generator 18.

In accordance with the invention, an auxiliary blocking mask 37 is placed within cathode-ray tube 17 between the parallax grid 38 and the electron gun assembly 31, in close proximity to parallax mask 38. The auxiliary blocking mask 37 may be composed of a material, such as an alloy of copper and nickel known as cupernickel, which is electrically conductive and suitable for use in a vacuum, and is provided with apertures or electronpenneable areas 39 which correspond specifically to and are individually larger than the apertures in the parallax mask. In an illustrative structure, it has been determined that if the spacing between the auxiliary blocking mask 37 and the parallax mask 38 is approximately .005", then the diameter of the apertures may be .02 and .01 for the auxiliary blocking mask and the parallax mask respectively. Blocking mask 37 may be supported within the enevlope in any convenient manner, as for example by being secured to the parallax grid-fluorescent screen assembly 38, 41. Blocking mask 37 is maintained at a suitable positive operating potential by connection to the positive terminal of a battery 42 or other suitable voltage source. The construction of tricolor cathode-ray tubes requires extreme care, and many of the construction details are omitted for clarity, since such details are well known in the art and constitute no part of the present invention.

Figure 3 is an enlarged fragmentary view useful in explaining the operation of the auxiliary blocking mask 37, which is placed between the point of origin of the electron beams and the parallax mask 38. In Figure 3, for purposes of simplicity and convenience, only one of the electron beams 36 is shown approaching auxiliary blocking mask 37, parallax grid 38, and target 41 comprising fluorescent elements R, B, and G corresponding to the primary colors red, blue, and green respectively. Target 41 is so arranged that the electron beam which passes successively through grids 37 and 38 may be directed to energize only the phophor elements of a single group; as shown, electron beam 36 is directed only to elements R of the red phosphor group. As the electron beam 36 scans the target 41, grid 37 intercepts a large proportion of those electrons which would impinge upon the parallax grid 38 in the absence of grid 37. Preferably, auxiliary blocking mask 37 is placed in close proximity to parallax grid 38, and the apertures in blocking mask 37 are only slightly larger than and are in registration with the apertures of parallax grid 38 so that about 50% of the electron beam current is collected by the auxiliary blocking mask. Consequently, the beam current collected by parallax grid 38 is correspondingly reduced, thus substantially precluding overheating and distortion of the parallax grid, even at substantially higher operating voltages than heretofore employed in color-image reproducers of the parallax grid type. In this manner, undesirable color contamination is substantially avoided and increased picture brightness is achieved.

Figure 4 shows the elements 37, 38, and 41 superimposed, as they appear from the center of scan in the field of the deflection yoke (scanning coils 33 of Figure 2). In the upper portion of the figure, only the tricolor screen or target 41 is shown, while in lower portions first the parallax grid 38 and then the auxiliary blocking mask 37 of the present invention are superimposed to indicate the geometrical relationships between these elements. From Figure 4, it is apparent that the apertures of grid 37 are larger than and are in registration with those of grid 38.

The construction of auxiliary blocking mask 37 may be accomplished through the use of any of several well known techniques for producing apertures in electrically ture brightness.

conductive plates. One method of doing this is to prepare thin cupernickel sheets for processing through a photoengraving technique. "5 he master pattern for photoengraving may be made by contact printing a grill three successive times on the same photographic plate; each successive exposure being made after the grill has been rotated through an angle of 60. Having thus obtained a suitable negative, the thin cupernickel sheet is coated with engravers enamel, exposed through the negative with ultra-violet light, and developed. The exposed enamel is insoluble but the unexposed enamel washes away to uncover the metal underneath. Ferricchloride etching solution is then applied to etch holes where the metal is exposed in this manner.

In some instances, it may be desirable to operate the fluorescent screen or target 41 at an elevated potential with respect tothe parallax grid 38 to achieve postselection acceleration and a consequent increase in pic- However, when this is done, secondary electrons originating at the parallax grid may bombard the target in a random manner, thus leading to color contamination and a loss of picture fidelity. In a tube constructed in accordance with the present invention, the potential of the auxiliary blocking mask may be made slightly more positive than that of the parallax grid, to attract secondary electrons originating at the parallax grid and thus prevent secondary electron bombardment of unselected color phosphors.

The present embodiment is not restricted to those types of color tubes in which the phosphor elements of different color characteristics are arranged in dot triads; for example, the invention is also useful in those color tubes in which the color phosphors are arranged on the target area in lines or strips. Furthermore, tubes embodying the invention are not limited to any specific type of color television reception but may be employed to equal advantage in either sequential or simultaneous color television systerns.

While a particular embodiment of the invention has been shown and described, modifications may be made, and it is intended in the appended claim to cover all such modifications as may fall within the true spirit and scope of the invention.

I .claim:

An image-reproducing device for use in a color television receiver comprising: a target assembly of the type comprising a luminescent screen having interspersed similar groups each consisting of a predetermined plurality of similar elemental target areas, each of said groups of target areas exhibiting a distinctive color-response characteristic to electron bombardment, and a parallax mask spaced from said luminescent screen and provided with a corresponding plurality of electron-permeable areas individually associated with one of said elemental target areas of each of said groups; means including at least one electron gun for projecting space electrons toward said target assembly with different angles of approach to selectively energize said groups of target areas; and an auxiliary blocking mask interposed between said electron-projecting means and said target assembly and provided with a plurality of electron-permeable areas individually larger than said electron-permeable areas of said parallax mask and in registration therewith; means for establishing a potential difference between said parallax mask and said luminescent screen; and means for maintaining said auxiliary blocking mask at a positive potential with respect to said parallax mask.

References Cited in the file of this patent UNITED STATES PATENTS 2,590,764 Forgue Mar. 25, 1952 2,619,608 Rajchman Nov. 25, 1952 2,659,026 Epstein Nov. 10, 1953 2,663,821 Law Dec. 22, 1953 

